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Negative pressure

 An exciting experiment

Imagine you are in a 0 pressure surrounding and think what will happen if you try capillary action there??

 Think think....

Well, ideally seeing, it should form a meniscus with a pressure difference of 2T/R. So, we will (theoretically) find that above the meniscus there is 0 pressure and below it there is -2T/R pressure (unit). Here T represents surface tension and R represents radius of curvature of surface. Well, wait as first glance u might think that is negative pressure possible??? And if yes then what does it signifies? It seems to be senseless at first. But for liquids and solids it does exist. 

Well, returning to our capillary action, we can't have such a scenario because the liquid will evaporate  until it achieves its surrounding's pressure greater than or equal to its vapour pressure and hence no 0 external pressure...hence no negative pressure.

But...but...but....

It can still be achieved if u take such a liquid whose vapour pressure is low than 2T/R and then exposing liquid to pressure equal to its vapour pressure then it will certainly stop it from vapourising and hence capillary action will be seen. Now, we'll again have a pressure difference of 2T/R above meniscus and below meniscus. This time pressure above the meniscus is equal to vapour pressure (VP) of liquid and below it will be VP - 2T/R. Now think about an interesting case which will arise when VD<2T/R....there is a certainity that we will have negative pressure.....whoa......Now, we should now begin to find a liquid whose vapour pressure is less than 2T/R. 

To be continued

:)

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